Nanostructured moulded bodies and layers and method for producing same

ABSTRACT

Described are nanostructured molded articles and layers which are produced by a wet chemical process comprising the following steps: 
     a) provision of a free-flowing composition containing solid nanoscaled inorganic particles having polymerizable and/or polycondensable organic surface groups; 
     b) introduction of said composition of step a) into a mold; or 
     b2) application of said composition of step a) onto a substrate; and 
     c) polymerization and/or polycondensation of the surface groups of said solid particles with formation of a cured molded article or a cured layer.

The present invention relates to nanostructured moulded articles andlayers as well as to processes for their production. Particularly, thepresent invention relates to nanostructured moulded articles and layerswhich can be produced by means of a wet chemical process.

Nanostructured materials have been known for quite a while. They areusually prepared by densification of nanoscaled particles havingdiameters in the lower nanometer range by a suitable process (see, e.g.,H. Gleiter, Nanocrystalline Materials, Pergamon Press, Oxford, 1989).This is done mostly under high pressure, taking advantage of the highdiffusion rates in the outer districts of the nanoscaled particles.Under the action of pressure (and as the case may be, simultaneousaction of elevated temperatures) a densification to form dense articlestakes place thereby. Corresponding wet chemical processes such as, e.g.,the sol-gel process usually result in porous gels since, although due tothe high surface activity of the particles a bonding thereof takesplace, a tight joining together of the particles and a filling of thegussets does not occur. Materials prepared by such processes areuniform, i.e., they have interfacial phases the composition whereof isnot (significantly) different from that of the particle phase (only thegaseous phase of the environment may be additionally present).

It has now surprisingly been found that if said nanoscaled particles areprovided with polymerizable and/or polycondensable organic surfacegroups and said surface groups are polymerized and/or polycondensed,systems of nanostructured materials equivalent or even superior to thosewhich have so far been prepared via the dry route are available via thewet chemical route. Particularly, highly transparent materials are alsoavailable via said route since due to the small distances between theparticles (one to a few nm) the correlation lengths for the Raleighscattering are not reached.

Subject of the present invention thus is a process for the production ofnanostructured moulded articles and layers comprising the followingsteps:

a) provision of a free-flowing composition which contains solidnanoscaled inorganic particles having polymerizable and/orpolycondensable organic surface groups;

1) introduction of the composition of step a) into a mould; or

2) application of the composition of step a) onto a substrate;

c) polymerization and/or polycondensation of said organic surface groupsof said solid inorganic particles with formation of a cured mouldedarticle or a cured layer.

It may be advantageous in many cases to conduct, subsequent to the abovestep c), a thermal post-treatment of said cured moulded article or saidcured layer, respectively, preferably at a temperature ranging from 60to 150° C., particularly from 80 to 130° C.

Alternatively or in addition thereto, a (further) thermal densificationof said moulded article or said layer, respectively, at a temperature ofat least 250° C., preferably at least 400° C. and particularly at least500° C., may be effected. In the case of a layer on a substrate thermaldensification may naturally only be carried out if the substratematerial can resist such high temperatures without impairment, as thisis the case with, e.g., glass and many metals and metal alloys,respectively (but also with some plastics).

In some cases it may be recommendable to carry out a (further) thermaldensification at temperatures ranging from 800 to 1500° C., preferably1000 to 1400° C.

(Post-)treatment at temperatures of at least 350° C. generally makes itpossible to utilize said solid nanoscaled inorganic particles as firmprecursor for the production of an exclusively inorganic solid.

In the present description and the appended claims the term “solidnanoscaled inorganic particles” is to denote particles having a meanparticle size (a mean particle diameter) not exceeding 200 nm,preferably not exceeding 100 nm and particularly not exceeding 70 nm. Aparticularly preferred range of particle sizes is from 5 to 50 nm.

The solid nanoscaled inorganic particles may consist of any material butpreferably they consist of metals and particularly of metal compoundssuch as (optionally hydrated) oxides, such as ZnO, CdO, SiO₂, TiO₂,ZrO₂, CeO₂, SnO₂, Al₂O₃, ln₂O₃, La₂O₃, Fe₂O₃, Cu₂O, Ta₂O₅, Nb₂O₅, V₂O₅,MoO₃ or WO₃; chalcogenides such as sulfides (e.g. CdS, ZnS, PbS andAg₂S), selenides (e.g. GaSe, CdSe and ZnSe) and tellurides (e.g. ZnTe orCdTe), halides such as AgCl, AgBr, Agl, CuCl, CuBr, Cdl₂ and PbI₂;carbides such as CdC₂ or SiC; arsenides such as AlAs, GaAs and GeAs;antimonides such as InSb; nitrides such as BN, AIN, Si₃N₄ and Ti₃N₄;phosphides such as GaP, InP, Zn₃P₂ and Cd₃P₂; phosphates, silicates,zirconates, aluminates, stannates and the corresponding mixed oxides(e.g. those having a perovskite structure such as BaTiO₃ and PbTiO₃).

Preferably, the solid nanoscaled inorganic particles employed in step a)of the process according to the present invention are those of oxides,sulfides, selenides and tellurides of metals and mixtures thereof.Particularly preferred according to the present invention are nanoscaledparticles of SiO₂, TiO₂, ZrO₂, ZnO, Ta₂O₅, SnO₂ and Al₂O₃ (in anymodification, particularly in the form of boehmite, AlO(OH)) as well asmixtures thereof.

Since the nanoscaled particles employable according to the presentinvention cover a broad range of refractive indices, the refractiveindex of a moulded article or a layer, respectively, can conveniently beset at the desired value by appropriately selecting said nanoscaledparticles.

The production of the nanoscaled solid particles employed according tothe present invention may be effected in usual manner, e.g., by flamepyrolysis, plasma processes, condensation processes in the gas phase,colloid techniques, precipitation processes, sol-gel processes,controlled nucleation and growth processes, MOCVD processes and(micro)emulsion processes. Said processes are described in detail in theliterature. Particularly, metals (for example following the reduction ofthe precipitation processes), ceramic oxide systems (by precipitationfrom solution) but also salt-like or multicomponent systems may, forexample, be used. The salt-like or multicomponent systems also encompasssemiconductor systems.

The preparation of said solid nanoscaled inorganic particles providedwith polymerizable and/or polycondensable organic surface groups may onprinciple be carried out via two different routes, i.e., on the one handby surface modification of preformed solid nanoscaled inorganicparticles and, on the other hand, by preparation of said solidnanoscaled inorganic particles using one or more compounds having suchpolymerizable and/or polycondensable groupings. Said two approaches willbe explained in more detail further below and in the examples.

Said organic polymerizable and/or polycondensable surface groups may beany groups known to the skilled person which can undergo a radical,cationic or anionic, thermal or photochemical polymerization or thermalor photochemical poly-condensation (optionally in the presence of asuitable initiator or catalyst, respectively). Surface groups which arepreferred according to the present invention are those having a(meth)acrylic, acrylic, vinylic or epoxy group, (meth)acrylic and epoxygroups being particularly preferred. Among the polycondensable groupshydroxy, carboxy and amino groups may particularly be cited, said groupsmaking it possible to obtain ether, ester and amide linkages betweensaid nanoscaled particles.

According to the present invention it is also preferred that saidorganic groups present on the surfaces of said nanoscaled particles andcomprising said polymerizable and/or polycondensable groups have arelatively low molecular weight. In particular, the molecular weight ofsaid (purely organic) groups should not exceed 500 and preferably notexceed 300, particularly preferred not exceed 200. Of course this doesnot exclude a significantly higher molecular weight of the compounds(molecules) comprising said groups (e.g. 1000 and more).

As already mentioned above the polymerizable/polycondensable surfacegroups may on principle be provided via two different routes. In thecase where a surface modification of previously prepared nanoscaledparticles is carried out, any compounds (preferably of low molecularweight) which on the one hand have one or several groups capable ofreacting or at least interacting with (functional) groups present on thesurfaces of said nanoscaled solid particles (such as OH groups in thecase of oxides) and on the other hand feature at least onepolymerizable/poly-condensable group are suitable for said purpose. Thusthe corresponding compounds may, for example, form both covalent andionic (salt-like) or coordination (complex) bonds with the surfaces ofsaid nanoscaled solid particles, while as examples of pure interactionsdipole-dipole interactions, hydrogen bonding and van der Waalsinteractions may be mentioned. The formation of covalent and/orcoordination bonds is preferred. Specific examples of organic compoundswhich may be used for the surface modification of said nanoscaledparticles or inorganic solid are, for example, unsaturated carboxylicacids such as acrylic acid and methacrylic acid, β-dicarbonyl compounds(e.g. β-diketones or β-carbonylcarboxylic acids) having polymerizabledouble bonds, ethylenically unsaturated alcohols and amines, epoxidesand the like. According to the present invention, hydrolyticallycondensable silanes having at least (and preferably) onenon-hydrolyzable radical featuring a polymerizable carbon-to-carbondouble bond or an epoxide ring are particularly preferred —especially inthe case of oxide particles. Preferably such silanes are of the generalformula (I):

X—R¹—SiR² ₃  (I)

wherein X is CH₂═CR³—COO, CH₂═CH oder glycidyloxy, R³ representshydrogen or methyl, R¹ is a divalent hydrocarbon radical having 1 to 10,particularly 1 to 6 carbon atoms which optionally contains one or moreheteroatomic groups (e.g. O, S, NH) separating adjacent carbon atoms,and the radicals R², the same or different from each other, are selectedfrom alkoxy, aryloxy, acyloxy and alkylcarbonyl groups as well ashalogen atoms (particularly F, Cl and/or Br).

Preferably said groups R² are identical and selected from halogen atoms,C₁₋₄ alkoxy groups (e.g. methoxy, ethoxy, n-propoxy, i-propoxy andbutoxy), C₆₋₁₀ aryloxy groups (e.g. phenoxy), C₁₋₄ acyloxy groups (e.g.acetoxy and propionyloxy) and C₂₋₁₀ alkylcarbonyl groups (e.g. acetyl).

Particularly preferred radicals R² are C₁₋₄ alkoxy groups and especiallymethoxy and ethoxy.

The radical R¹ preferably is an alkylene group, particularly one having1 to 6 carbon atoms such as, e.g., ethylene, propylene, butylene andhexylene. If X represents CH₂═CH, R¹ is preferably methylene and in thiscase may also represent a mere bond.

Preferably X is CH₂═CR³—COO (R³ preferably being CH₃) or glycidyloxy.Particularly preferred silanes of general formula (I) thus are(meth)acryloyloxyalkyltrialkoxysilanes such as, e.g.,3-methacryloyloxypropyltri(m)ethoxysilane andglycidyloxyalkyltrialkoxysilanes such as3-glycidyloxypropyltri(m)ethoxysilane.

If said nanoscaled particles of inorganic solid have already beenprepared by using one or more compounds featuringpolymerizable/polycondensable groups a subsequent surface modificationmay be dispensed with (although same is, of course, possible asadditional measure).

The in situ preparation of solid nanoscaled inorganic particles havingpolymerizable/polycondensable surface groups will in the following beexplained for the case of SiO₂ particles. For said purpose said SiO₂particles may, for example, be prepared according to the sol-gel processusing at least one hydrolytically polycondensable silane featuring atleast one polymerizable/polycondensable group. Suitable examples of suchsilanes are the silanes of general formula (I) already described above.Said silanes are preferably used either alone or in combination with asuitable silane of general formula (II)

SiR² ₄  (II)

wherein R² has the meaning defined above. Preferred silanes of the abovegeneral formula (II) are tetramethoxysilane and tetraethoxysilane.

It is of course also possible to use, in addition or alternatively tothe silanes of general formula (II), other silanes, e.g., those having a(non-hydrolyzable) hydrocarbon group without any functional group suchas, e.g., methyl or phenyl trialkoxysilanes. Especially if an easy toclean surface of the moulded article or the layer is desired, it may berecommendable to use, apart from the silanes of general formula (I) andoptionally of general formula (II), a certain amount (e.g. up to 60 andparticularly up to 50% by moles based on the total of silanes employed)of silanes having fluorine containing (non-hydrolyzable) radicals,particularly hydrocarbon radicals. Particularly preferred here aresilanes of general formula (I), wherein R² is defined as above, R¹ is anethylene group and X is a perfluoroalkyl group having 2 to 12,preferably 4 to 8 carbon atoms. Further silanes employable for saidpurpose are, for example, those having (per)fluorinated aryl(particularly phenyl) groups. Such fluorinated silanes may, of course,also be employed for the surface modification of previously preparedsolid nanoscaled inorganic particles.

The material employed in step a) of the process according to the presentinvention is present in the form of a still free-flowing composition(suspension). The liquid component of said composition is composed of,e.g., water and/or (preferably water-miscible) organic solvent and/orcompounds employed or formed in the course of the preparation of thenanoscaled particles or the surface modification thereof (e.g. alcoholsin the case of alkoxysilanes). Suitable organic solvents which mayoptionally be employed additionally are, for example, alcohols, ethers,ketones, esters, amides and the like. However, an (additional) componentof said free-flowing composition may, for example, also be constitutedby at least one monomeric or oligomeric species featuring at least onegroup capable of reacting (polymerizing or polycondensing, respectively)with polymerizable/polycondensable groups present on the surface of saidnanoscaled particles. As examples of such species monomers having apolymerizable double bond such as acrylic acid esters, methacrylic acidesters, styrene, vinyl acetate and vinyl chloride may be cited. As(preferably employed) monomeric compounds having more than onepolymerizable bond there may particularly be mentioned those of generalformula (III):

(CH₂═CR³—COZ)_(n)—A  (III)

wherein

n=2, 3 or 4, preferably 2 or 3, and particularly 2;

Z=O or NH, preferably O;

R³=H, CH₃;

A=n-valent hydrocarbon radical having 2 to 30, particularly 2 to 20carbon atoms which may feature one or more heteroatomic groups, eachlocated between adjacent carbon atoms (examples of such heteroatomicgroups being O, S, NH, NR (R≦hydrocarbon radical), preferably O).

Furthermore, the hydrocarbon radical A may carry one or moresubstituents, preferably selected from halogen (particularly F, Cland/or Br), alkoxy (particularly C₁₋₄ alkoxy), hydroxy, optionallysubstituted amino, NO₂, OCOR⁵, COR⁵ (R⁵═C₁₋₆ alkyl or phenyl).Preferably, however, the radical A is unsubstituted or substituted byhalogen and/or hydroxy.

In a particularly preferred embodiment of the present invention, A isderived from an aliphatic diol, an alkylene glycol, a polyalkyleneglycol or an optionally alkoxylated (e.g. ethoxylated) bisphenol (e.g.bisphenol A).

Further examples of employable compounds having more than one doublebond are allyl(meth)acrylate, divinylbenzene and diallylphthalate. Alsoemployable is, for example, a compound having two or more epoxy groups(in case epoxide containing surface groups are employed), e.g.,bisphenol A diglycidylether, or also an (oligomeric) precondensate of anepoxy group containing hydrolyzable silane (e.g.glycidoxypropyltrimethoxysilane).

If additional monomeric compounds having polymerizable/poly-condensablegroups are employed they preferably account for not more than 40%,particularly not more than 30%, and particularly preferred not more than15% by weight of the total solids content of the free-flowingcomposition of step a).

In step b) of the process according to the present invention saidfree-flowing composition of step a) is either introduced into a suitablemould in order to produce a moulded article, or is applied onto adesired substrate in order to coat said substrate completely orpartially. The coating methods suitable for said purpose are the commonones known to the skilled person. Examples thereof are dip coating,spray coating, doctor blade coating, painting, brushing, spin coating,etc.

Prior to introduction into the mould or application onto a substrate,said free-flowing composition may be adjusted to a suitable viscosity,for example by adding solvent or evaporating volatile components(particularly solvent already present).

Substrates made of any material, particularly of plastics, metals andglass, are suitable for being coated with the free-flowing compositionof step a) of the process according to the present invention. Prior tothe application of said free-flowing composition said substratematerials may optionally be subjected to a surface treatment (e.g.degreasing, roughening, corona discharge, treatment with a primer,etc.). Especially when substrates made of plastics are coated a suitableadhesion may be provided by adding a suitable monomeric polymerizablecompound and/or according to the preferred embodiment described in moredetail below.

Among the metal substrates which may be coated according to the presentinvention metals such as aluminum, copper, zinc, nickel and chromium,and metal alloys such as (stainless) steel, brass and bronze may bementioned as examples. Examples for suitable substrates made of plasticsare those made of polycarbonate, polyesters, polyamides, polystyrene,poly(meth)acrylates (e.g. polymethylmethacrylate), PVC, polyolefins(such as polyethylene and polypropylene), rubbers (ABS, NBS, etc.) andpolyphenylenesulfide, to name but the most important ones.

In step c) of the process according to the present invention apolymerization and/or polycondensation of thepolymerizable/polycondensable surface groups of said solid nanoscaledinorganic particles (and, optionally, of thepoylmerizable/polycondensable groups of the monomeric or oligomericspecies additionally employed) is carried out. Saidpolymerization/polycondensation may be carried out in a manner known tothe person skilled in the art. Examples of suitable processes arethermal, photochemical (e.g. by means of UV radiation), electron beamcuring, laser curing, room temperature curing, etc. Such apolymerization/poly-condensation is optionally effected in the presenceof a suitable catalyst or starter (initiator), respectively, which isadded to said free-flowing composition of step a) at the latestimmediately before the introduction thereof into the mould or theapplication thereof onto the substrate, respectively.

As starters/starter systems the conventional ones known to the skilledperson are envisaged, including radical photostarters, radicalthermostarters, cationic photostarters, cationic thermostarters and anycombination thereof.

Specific examples of employable radical photostarters are Irgacure® 184(1-hydroxycyclohexylphenylketone), Irgacure® 500(1-hydroxycyclohexylphenylketone, benzophenone) and otherphotoinitiators of the Irgacure® type available from the companyCiba-Geigy; Darocur® 1173, 1116, 1398, 1174 and 1020 (available from thecompany Merck); benzophenone, 2-chlorothioxanthone,2-methylthioxanthone, 2-isopropylthioxanthone, benzoin,4,4′-dimethoxybenzoin, benzoin ethylether, benzoin isopropylether,benzil dimethylketal, 1,1,1-trichloroacetophenone, diethoxyacetophenoneand dibenzosuberone.

Examples of radical thermostarters are, i.a., organic peroxides in theform of diacylperoxides, peroxydicarbonates, alkylperesters,alkylperoxides, perketals, ketoneperoxides and alkylhydroperoxides aswell as azo compounds. As specific examples thereof dibenzoylperoxide,tert-butylperbenzoate and azobisisobutyronitrile may particularly bementioned.

An example for a cationic photostarter is Cyracure® UVI-6974, while1-methylimidazole is a preferred cationic thermostarter.

Said starters will be employed in the conventional amounts known to theskilled person (preferably 0.01-5%, particularly 0.1-2% by wt. based onthe total solids content of the free-flowing composition of step a)).Under certain circumstances it is of course possible to completelydispense with the starter, e.g., in the case of electron beam or lasercuring.

Said polymerization/polycondensation of step c) of the process accordingto the present invention is preferably carried out thermally or byirradiation (particularly with UV light). Particularly preferred is aphotochemical polymerization/polycondensation or a combination ofthermal and photochemical polymerization/polycondensation, respectively.

Said polymerization/polycondensation may be preceded by a removal offurther volatile, non-polymerizable/non-polycondensable compounds fromthe composition present in the mould or on the substrate, respectively.Said removal of volatile components may, however, be effected also oradditionally, respectively, at the polymerization/polycondensation stageor thereafter.

In the following, a typical process according to the present inventionwhich may result in transparent moulded articles will be outlined by wayof example, the value ranges and procedures given being of generalvalidity, irrespective of the specific materials employed.

Nanoscaled particles of, e.g., SiO₂, TiO₂, ZrO₂ and other oxidic orsulfidic materials (particle size 30 to 100 nm, preferably 40 to 70 nm)are dispersed in a solvent (for example, in a lower alcohol such asmethanol, ethanol, propanol) at a concentration of 1 to 20%, preferably5 to 15% by weight, and added thereto is a surface modifier havingpolymerizable/polycondensable groups in an amount of preferably 2 to25%, particularly 4 to 15% by weight (based on the total solidscontent). In the case of, for example, silanes said surface modificationmay be effected by stirring at room temperature for several hours.Subsequently a monomeric or oligomeric material havingpolymerizable/polycondensable groups and being compatible with saidsurface modifier and the surface groups, respectively, may optionally beadded in an amount of, for example, up to 20%, preferably 4 to 15% byweight (based on the total solids content). Following the addition ofone or more suitable starters (each in an amount of, e.g., 0.01 to 1%,preferably 0.1 to 0.5% by weight, based on the total solids content) thesolvent is partially removed (preferably 50 to 98%, particularly 75 to95% thereof. The still free-flowing composition is then placed in thedesired mould, whereafter the residual solvent is removed. Then a firstcuring operation is carried out. In order to reduce the reaction times,a photopolymerization is preferably employed; any light sources,particularly sources emitting UV radiation, are employable here (e.g.mercury lamps, xenon lamps, laser light, etc.). Curing by laser lightpermits application for the so-called “rapid prototyping”. Following athermal post-curing for the further densification of the structure (e.g.0.5-4 hours at 70 to 150° C., preferably 1-2 hours at 80 to 100° C.) agreen compact is obtained. Said green compact may be heated to atemperature of, e.g., 500° C., for example within 2 to 10 hours,preferably 3 to 5 hours, and kept at said temperature, e.g. for 2 to 10hours (preferably 3 to 5 hours). In most cases said step results in thecomplete loss of said organic (carbon containing) groups in said mouldedarticle. For final densification said moulded article may then be heatedto a temperature of, e.g., 1400° C., for example within 2 to 10 hours(preferably 3-5 hours), and be kept at said temperature for, e.g., 1 to5 hours (preferably 2-3 hours). Thereby a colorless, transparent, purelyinorganic moulded article may be obtained.

The production of a layer may, for example, be carried out by adding tosols featuring, for example, oxidic or sulfidic nanoparticleshydrolyzable silanes having polymerizable/polycondensable groups at aconcentration of preferably not more than 100%, particularly not morethan 75% by weight (based on said nano-particles). Following theadjustment of the viscosity by addition or removal, respectively, ofsolvent (e.g. alcohol) and after the addition of a photoinitiator (e.g.at a concentration of 5% by weight based on the silane employed) acuring of the layer on the selected substrate with preferably UV lightresults in transparent, crack-free and homogeneous layers. A thermalpost-treatment at, for example, 60 to 100° C. usually results in asignificant improvement in the layer properties; said post-treatment is,however, not indispensable. The layers thus produced have good abrasionresistance. Since in said process the thermal post-treatment may becarried out at relatively low temperatures, substrates having lowthermal stability may also be used without any problems. As alreadymentioned above, the adhesion of the layer to the substrate may beadjusted by varying the amount and type of silane employed and by addingan additional organic monomer (methacrylate, acrylate, etc.) at lowconcentrations (for example, <5% by wt.), thereby, for example, bothglass and plastics may be coated. The co-use of the fluorinated silanesmentioned above in the surface modification furthermore results ineasy-to-clean layers on the corresponding substrates and in a reductionof the surface energy, respectively, while the addition of, e.g.,surfactants can increase the surface energy.

According to a preferred embodiment of the present invention, especiallyfor the coating of substrates made of plastics, nanoparticles(particularly those of AlOOH, ZrO₂, TiO₂ and the like) are dispersed atrelatively high concentrations (usually at least 15% and preferably atleast 20% by wt. or at least 7% or 10%, respectively, by volume,preferred upper limits being 80% by wt., particularly 60% by wt. or 40%by volume, particularly 25% by volume, respectively) in a liquid systemcomprising as essential component at least one hydrolyzable silanefeaturing a polymerizable/polycondensable group (e.g. one of the abovegeneral formula (I)) and subsequently a (conventional) prehydrolysis ofsaid silane is carried out. In addition to said silane featuring apolymerizable/polycondensable group other hydrolyzable components mayoptionally be present, particularly other (optionally fluorinated)silanes (e.g. those of the above general formula (II)) and/orhydrolyzable compounds (e.g. alkoxides, halides) of metals of the mainand sub-groups of the Periodic Table (e.g. Al, Ti, Zr). After theprehydrolysis, further species having more than one (preferably two)copolymerizable/copolycondensable groups (in particular those of theabove general formula (III), preferably in amounts of up to 40%,particularly up to 30% and particularly preferred up to 15% by wt.) maybe added. As polymerizable groups (meth)acrylate groups are particularlypreferred. Prior to the application onto a plastic substrate a solvent(e.g. an alcohol) may be added to said system in order to adjust theviscosity thereof, as well as conventional paint additives (see below).Although the resulting coating composition may be cured thermally(preferably following the addition of a corresponding thermostarter) ithas surprisingly been found that when using a photoinitiator (preferablyin the conventional amounts given above) even a (sole) photochemicalcuring (preferably by UV light) results in a highly scratch-resistant,transparent layer which, moreover, shows good adhesion to most plasticssubstrates without pretreatment of the surfaces thereof (e.g. in thecase of polycarbonates, polystyrene, poly(meth)acrylate, etc.).

Of course, dyes, pigments, matting agents, etc. may be added to thecorresponding coating composition if a colored or non-transparent,respectively, layer is desired. Examples of further conventionaladditives for compositions of the described type are flow additives, UVabsorbers, antioxidants (e.g. HALS), antistatic agents, surfactants (forhydrophilic surfaces) and fluorinated compounds (forhydrophobic/oleophobic surfaces).

An additional advantage of proceeding in the manner just described isthat a solvent exchange prior to the application, as often described inthe prior art, is not necessary since one preferably operates withoutseparately added solvent (except in order to adjust the viscosity afterprehydrolysis).

The moulded articles available according to the present invention aresuitable for a number of applications. Only by way of example, thefollowing fields of application may be mentioned in the present context:rapid prototyping, e.g. in the medical field (for prostheses, simulationof organs), prototyping in the field of automobiles (design models,motor components, etc.), optical elements, development of dies,development of testing procedures.

In the case of the layers according to the present inventionscratch-resistant coatings having functional properties (anti-reflex,protection against corrosion, hydrophilic properties, hydrophobicproperties, antistatic layers) may be mentioned. Coatable materialsinclude those made of transparent and non-transparent plastics, glass,metals, stone, wood, paper and textiles but are not limited thereto.

The above coating compositions are particularly suitable for the coatingof constructions and parts thereof; means of locomotion and of transportand parts thereof; operating equipment, devices and machines forcommercial and industrial purposes and research, and parts thereof;domestic articles and household equipment and parts thereof; equipment,apparatus and accessories for games, sport and leisure, and partsthereof; and also instruments, accessories and devices for medicalpurposes and the sick. Said compositions are also highly suitable forthe provision of interference layers. Specific examples of coatablematerials and articles are indicated below.

Constructions (Especially Buildings) and Parts Thereof

Interior and exterior facings of buildings, floors and staircases madeof natural stone, concrete, etc., floor coverings of plastic, fifted andloose carpets, base boards (skirting boards), windows (especially windowframes, window sills, glazing of glass or plastic and window handles),Venetian blinds, roller blinds, doors, door handles, WC, bath andkitchen fittings, shower cabinets, sanitary modules, lavatories, pipes,radiators, mirrors, light switches, wall and floor tiles, lighting,letter boxes, roof tiles, guttering, aerials, satellite dishes,handrails of balconies and moving stairways, architectural glazing,solar collectors, winter gardens, walls of lifts; memorials, sculpturesand, generally, works of art made of natural stone (e.g. granite,marble), metal, etc., especially those erected outdoors.

Means of Locomotion and of Transport (e.g. Car, Truck, Bus, Motorbike,Moped, Bicycle, Railway, Tram, Ship and Aircraft) and Parts Thereof

Headlamps, interior and exterior mirrors, windscreens, rear windows,side windows, mudguards of bicycles and motorbikes, plastic visors ofmotorbikes, instruments of motorbikes, seats, saddles, door handles,steering wheels, tire rims, fuel-tank ports (especially for diesel),number plates, luggage racks, roof containers for cars, and cockpits.

Operating Equipment, Devices and Machines for Commercial and IndustrialPurposes and Research and Parts Thereof

Moulds (e.g. casting moulds, especially those made of metal), hoppers,filling units, extruders, water wheels, rollers, conveyor belts,printing presses, screen-printing stencils, dispending machines,(machine) housings, injection-moulded components, drill bits, turbines,pipes (interior and exterior), pumps, sawblades, screens (for examplefor scales), keyboards, switches, knobs, ball bearings, shafts, screws,displays, solar cells, solar units, tools, tool handles, containers forliquids, insulators, capillary tubes, lenses, laboratory equipment (e.g.chromatography columns and hoods) and computers (especially casings andmonitor screens).

Domestic Articles and Household Equipment and Parts Thereof

Furniture veneers, furniture strips, rubbish bins, toilet brushes, tablecloths, crockery (for example made of porcelain and stoneware),glassware, cutlery (e.g. knives), trays, frying pans, saucepans, bakingsheets, cooking utensils (e.g. cooking spoons, graters, garlic presses,etc.), inset cooking plates, hotplates, ovens (inside and outside),flower vases, covers for wall clocks, TV equipment (especially screens),stereo equipment, housings of (electrical) domestic equipment, pictureglass, Christmas tree baubles, wall paper, lamps and lights, upholsteredfurniture, articles of leather.

Equipment, Apparatus and Accessories for Games, Sport and Leisure

Garden furniture, garden equipment, greenhouses (especially glazed),tools, playground equipment (e.g. slides), balls, airbeds, tennisrackets, table-tennis bats, table-tennis tables, skis, snow boards, surfboards, golf clubs, dumb-bells, benches in parks, playgrounds, etc.,motor bike clothing, motor bike helmets, ski suits, ski boots, skigoggles, crash helmets for skiers, wet-suits and diving goggles.

Instruments, Accessories and Devices for Medical Purposes and the Sick

Prostheses (especially for the limbs), implants, catheters, analprostheses, dental braces, false teeth, spectacles (lenses and frames),medical instruments (for operations and dental treatment), plastercasts, clinical thermometers and wheel-chairs, and also, quitegenerally, hospital equipment.

In addition to the above articles it is also possible, of course, tocoat other articles and parts thereof, advantageously, with the abovecoating compositions, examples being jewellery, coins, works of art (forexample paintings), book covers, gravestones, urns, signs (for exampletraffic signs), neon signs, traffic light pillars, CDs, wet-weatherclothing, textiles, postboxes, telephone booths, shelters for publictransport, protective goggles, protective helmets, films (for examplefor packaging foods), telephones, seals for water taps, and quitegenerally all articles produced from rubber, bottles, light-, heat- orpressure-sensitive recording materials (before or after recording, forexample photos), and church windows.

With Respect to the Interference Layers Mentioned Above the FollowingExemplary Applications May be Cited

Optical filters: anti-reflex and reflex filters in the field of glasses,displays, screens, semiconductor lasers, microlens coatings, solarcells, “damage-resistant” laser layers.

Holographic layers: light guide systems, recording of information, lasercoupling, waveguides, decoration and architecture.

Embossable layers: dereflection systems, focussing in detector fields,lighting of flat screens, image formation in photocopying devices, fiberoptics (input of light).

Lithography: production of microoptical components of waveguides,gratings, pinholes, diffraction gratings (point lattices), as well as inthe fields of display technology, fiber chip coupling and imagingoptics.

Bakable layers: color filters on metals, interference filters on glasssuch as, e.g., band pass filters, anti-reflex filters, absorptionfilters and beam splitting devices.

The following examples serve to further illustrate the presentinvention.

EXAMPLE 1 Production of a Transparent SiO₂ Moulded Article Free ofOrganic Components

SiO₂ particles (OX-50, primary particle size 40 nm) are dispersed inisopropanol at a concentration of 10% by wt. with stirring andultrasound for about 30 minutes. Thereafter,3-methacryloxypropyltrimethoxysilane (MPTS) is added slowly and understirring in an amount of 6% by wt. based on the SiO₂ content. Asilanization of said SiO₂ particles is achieved by stirring at 50° C.for 3 hours. Then 6% by wt. (based on the total solids content) oftetraethyleneglycol dimethacrylate (TEGDMA) are added, and stirring iscontinued for another 15 minutes. Finally, 2% by moles of Irgacure® 184(Ciba-Geigy) per mole of double bonds are added as photostarter for theUV polymerization. Subsequently the solvent is partially removed invacuo (distilling off the alcohol completely results in gelling so thata free-flowing and pourable, respectively, suspension cannot be obtainedanymore). The suspension thus obtained may then serve directly for theproduction of bulk materials by photopolymerization.

For said purpose, said SiO₂/MPTS/TEGDMA system is poured into a mouldmade of polyethylene. The viscous sol is again treated in vacuo (100mbar) for 1 hour at 25° C. in order to degasify it. A combinded UV/IRdryer (Beltron Company) is used to crosslink the organic components. Theoutput of the mercury lamps is 400 mW/m² each. The entirephotopolymerization of a bulk of 5 mm in thickness is achieved by anexposure amount of 240 J/cm². Said photo-polymerization results in adimensionally stable article. A crackless drying operation of thephotopolymerized bulk is carried out by treatment in an oven at 80° C.within one hour. Thereby a solvent-free and binder-containing SiO₂moulded article corresponding to a ceramic green compact is obtained. Inorder to burn out the residual organic components, the temperature ofthe oven is increased from 80° C. to 500° C. within 3 hours, the lattertemperature being maintained for another 3 hours. This leads to a porousSiO₂ bulk which is free of organic groups, as can be concluded from IRspectroscopical measurements. Finally, the temperature is increased from500° C. to 1400° C. within 3 hours and the latter temperature is thenmaintained for another 2 hours. Thus, a transparent moulded article isfinally obtained.

EXAMPLE 2 Production of a Transparent ZrO₂ Moulded Article Free ofOrganic Components

Nanoscaled zirconium oxide particles (“TOSOH Zirconia TZ-8Y” having aprimary particle size of 90 nm) are dispersed in isopropanol withstirring and under the action of ultrasound. For surface modification,3.2% by wt. (based on the content of ZrO₂) of MPTS are added to saidsuspension with stirring. A silanization of the ZrO₂ particles isachieved after 3 hours of stirring at 50° C. Thereafter, 3.2% by wt.(based on the content of ZrO₂) of TEGDMA are added, and stirring iscontinued for another 15 minutes at 20° C. As photostarter, 3% by molesof Irgacure® 184 per mole of double bonds are then added. This isfollowed by a partial removal of the solvent in vacuo. The free-flowingsuspension thus obtained serves directly for the production of bulkmaterials by photopolymerization. In order to obtain a moulded articlehaving a thickness of 5 mm, an output of 350 J/cm² is employed.

Crackless drying of the photopolymerizable bulk is achieved by treatingsaid photopolymerized moulded article in an oven at 80° C. within 30minutes. This results in a solvent-free and binder-containing ZrO₂ bulkcorresponding to a ceramic green compact. In order to burn out theresidual carbon content, the temperature of the oven is raised from 80°C. to 450° C. within 3 hours, whereafter the latter temperature ismaintained for another 3 hours. A porous ZrO₂ bulk free of organicgroups is thus obtained. Finally, the temperature is increased from 450°C. to 1400° C. within 3 hours and maintained at the latter value foranother 4 hours. The sintered moulded article obtained thereby istranslucent to opaque.

EXAMPLE 3 Synthesis of a Sol for the Production of Layers of HighReflective Index

86.861 g of TiO₂ sol (3.5% by wt. of TiO₂ in isopropanol; particle size:5 nm) are added to 1.989 g of tributylphosphate and stirring isconducted for 1 hour. Then a solution of 1.2 g of distilledγ-glycidyloxypropyltrimethoxysilane (GPTS) in 100 g of2-isopropoxyethanol is added dropwise at 100° C. to said sol. After 1hour of stirring the mixture is cooled to room temperature and 0.8775 gof hydrolyzed GPTS (prepared by adding 2.70 g of 0.1 N HCl to 23.63 g ofdistilled GPTS and stirring for 24 hours and subsequent distilling offof low molecular weight reaction products at 3 mbar) is added thereto.After 15 minutes of stirring the mixture in vacuo (3 mbar), the same issubjected to distillation and subsequently diluted with 120 g of2-isopropoxyethanol. Thus a transparent, agglomerate-free sol isobtained.

EXAMPLE 4 Synthesis of a Sol for the Production of Layers of LowRefractive Index

To a mixture of 23.63 g of GPTS (distilled) and 12.45 g oftetraethoxysilane (TEOS) there are added 2.88 g of 0.1 N HCl to effecthydrolysis and condensation. Then the resulting reaction mixture isstirred at 20° C. for 24 hours, and then subjected to distillation invacuo (at 3 mbar) in order to remove components of lower molecularweight. Subsequently the remaining reaction product is diluted with 50 gof isopropoxyethanol as solvent.

EXAMPLE 5 Synthesis of a Sol for the Production of Layers of LowRefractive Index and Additional Easy-to-Clean Function

Under stirring, 26.63 g of distilled GPTS are mixed with 8.30 g of TEOSand 0.11 g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FTS) for 15minutes. The resulting sol is hydrolyzed and condensed at 20° C. with4.5 g of 0.1 N HCl for 4 hours and with stirring. Thereafter, 52.10 g ofisopropoxyethanol and 0.53 g of phosphoric acid are added and stirringis continued at 20° C. for another 2 hours.

EXAMPLE 6 Production of a Layer on Glass with the Sol of Example 3

To the sol of Example 3, 0.08 g of Cyracure® UVI-6974 (Ciba-Geigy) and0.02 g of 1-methylimidazole are added. After intensive stirring themixture is filtered and can then be employed as coating composition.Glass plates (10 cm×10 cm×2 mm) are cleaned with 2-propanol and dried inair prior to the coating operation.

The coating composition is applied onto the substrate in a definedmanner by spin coating. The layer thickness is controlled by therotational speed of the substrate.

A combined UV/IR dryer (Beltron Company) is used for curing the layer.The apparatus used features two mercury lamps for irradiation with UVlight, a IR radiation device the output whereof can be used to controlthe surface temperature, and a conveyor belt on which the substrates canbe passed under said UVIR irradiation device with defined speed. Theoutput of the mercury lamps is 400 mW/cm² each.

The IR irradiation device is adjusted to 120° C., the speed of theconveyor belt is 2.6 m/min, and the coated substrates are passed underat these setpoints for a total of three times.

The last curing step is a thermal post-treatment at 120° C. in acirculating air drying cabinet for 15 minutes.

EXAMPLE 7 Production of a Layer on Polycarbonate (PC) Using the Sol ofExample 3

Using the coating material of Example 3, polycarbonate plates (10 cm×10cm×2 mm; pretreatment as described in Example 6) are coated and curedaccording to the process of Example 6. Differences: the IR irradiationdevice is set at 100° C., and the last curing step is a thermalpost-treatment at 100° C. in a circulating air drying cabinet for 30minutes.

EXAMPLE 8 Production of a Layer on Polymethylmethacrylate (PMMA) Usingthe Sol of Example 3

Using the coating material of Example 3, polymethylmethacrylate plates(10 cm×10 cm×2 mm; pretreatment as described in Example 6) are coatedand cured according to the process of Example 6. Differences: no IRirradiation, and the last curing step is a thermal post-treatment at 80°C. in a circulation air drying cabinet for 60 minutes.

EXAMPLE 9 Production of a Layer on PC Using the Sol of Example 4

To the coating material of Example 4 there are added 0.72 g of Cyracure®UVI-6974, 0.36 g of 1-methylimidazole and 10 g of a 0.02 percent byweight solution of aluminum tributoxyethanolate in 2-isopropoxyethanoland thoroughly mixed therewith. The necessary dilution is effected byadding 50 g of 2-isopropoxyethanol. Using said coating material,polycarbonate plates (see Example 7) are coated and cured according tothe process of Example 7. Differences: the substrates are passed underfour times at a speed of the conveyor belt of 2 m/min, and the lastcuring step is a thermal post-treatment at 100° C. in a circulating airdrying cabinet for 60 minutes.

EXAMPLE 10 Production of a Layer on PMMA Using the Sol of Example 4

The procedure of Example 9 is followed, but without use of the IRirradiation device. The last curing step is a thermal post-treatment at70° C. in a circulating air drying cabinet for 60 minutes.

EXAMPLE 11 Production of a Layer on PC Using the Sol of Example 5

The coating material according to Example 5 is provided with initiatorsaccording to Example 8 and cured according to the process described inExample 8.

Properties of the Layers Produced in Examples 6 to 11

Test Methods:

Refractive Index: Ellipsometric

Transmission (500 nm): Spectroscopic (coating the substrates on oneside)

Reflection (550 nm): Spectroscopic (backside of substrates uncoated andblackened)

Adhesion (layer on substrate): Cross-cut adhesion test and tape testaccording to DIN 53151 and DIN 58196

The values thus obtained are summarized in the following table.

Refractive Example Substrate index Transmission Reflection No. material(550 nm) [%] [%] Adhesion 6 Glas 1.91 78.5 20 0/0 7 PC 1.91 81 19 0/0 8PMMA 1.91 78.5 20 0/0 9 PC 1.47 91 8 0/0 10 PMMA 1.47 91 8 0/0 11 PC1.44 95 2.5 0/0

EXAMPLE 12 Coating of Substrates Made of Plastic

248.8 g (1 mole) of MPTS there are added with stirring 136.84 g (43% byweight based on the total solids content) of AlOOH nanopowder (Sol P3,15 nm, Degussa). Hydrolysis is effected by slowly adding thereto 36 g (2moles) of deionized water and 2.5 hrs of refluxing at 100° C. The cooledprehydrolysate is diluted to a solids content of 45% with 282 g of1-butanol, and 3.5 g (0.5% by wt.) of Byk®-306 are added thereto asleveling agent. For UV polymerization, 5.46 g (3% by moles based on thedouble bonds present) of benzophenone are added as photostarter. Theapplication of the coating system onto various plastic materials iseffected by spin coating. The curing of the layer is achieved by UVirradiation for 2 minutes by mercury lamp.

The coating shows good adhesion (CC/TT=0/0) without pretreatment of thesubstrate e.g. on PMMA. After 1000 cycles (Taber-Abraser, CS-10F, 500g/roll) the sctratch-resistant coating shows an abrasion hardness of11%.

EXAMPLE 13 Coating of Substrates Made of Plastic

The procedure of Example 12 is repeated with the exception that inaddition to benzophenone 1.05 g (1% by moles) of diethanolamine are usedas accelerator.

The coating shows good adhesion (CC/TT=0/0) without pretreating thesubstrate, e.g. on PMMA. After 1000 cycles (Taber-Abraser, CS-10F, 500g/roll) the scratch-resistant coating has an abrasion hardness of 9%.

EXAMPLE 14 Coating of Substrates Made of Plastic

To 248.8 g (1 mole) of MPTS there are added with stirring 99.52 g (31%by wt. based on the total solids content) of AlOOH nanopowder (Sol P3,15 nm, Degussa). Hydrolysis is effected by slowly adding thereto 36 g (2moles) of deionized water and 2.5 hrs of refluxing at 100° C. To thecooled prehydrolysate there are added 49.5 g (15% by moles) of TEGDMAand 3.9 g (0.5% by wt.) of Byk®-306 as leveling agent, and the mixtureis diluted to a solids content of 45% with 343 g of 1-butanol. For UVpolymerization, 0.6 g (2.5% by moles based on the double bonds present)of benzophenone are added as photostarter. The application of thecoating system onto various plastic materials is effected by spincoating. The curing of the layer is carried out by UV irradiation for 2minutes by means of a mercury lamp.

The coating shows good adhesion (CC/TT=0/0) without pretreatment of thesubstrate, e.g. on PMMA. After 1000 cycles (Taber-Abraser, CS-10F, 500g/roll) the scratch-resistant coating has an abrasion hardness of 15%.The dimethacrylate results in an increase in the flexibility and thewater stability of the coating. (Maintenance at 65° C. in deionizedwater>14 days, without dimethacrylate 7 days).

What is claimed is:
 1. A process for producing a nanostructured mouldedarticle or layer, comprising the following steps: (a) providing afree-flowing composition containing solid nanoscale inorganic particleshaving polymerizable and/or polycondensable organic surface groupsthereon; (b1) introducing the composition of step (a) into a mould; or(b2) applying the composition of step (a) onto a substrate; and (c)polymerizing and/or polycondensing the surface groups of the solidparticles, thereby forming a nanostructured moulded article or layer. 2.A process of claim 1, comprising the additional step of thermallypost-treating the nanostructured moulded article or layer of step (c).3. A process of claim 2 where the step of thermally post-treating thenanostructured moulded article or layer is carried out at a temperatureranging from 60° C. to 150° C.
 4. A process of claim 1, comprising theadditional step of thermally densifying the nanostructured mouldedarticle or layer.
 5. A process of claim 4 where the step of thermallydensifying the nanostructured moulded article or layer is carried out ata temperature of at least 20° C.
 6. A process of claim 5 where the stepof thermally densifying the nanostructured moulded article or layer iscarried out at a temperature of at least 400° C.
 7. A process of claim 1where the solid nanoscale inorganic particles are particles of metalcompounds.
 8. A process of claim 7 where the solid nanoscale inorganicparticles are particles of the oxides, sulfides, selenides, andtellurides of metals, and mixtures thereof.
 9. A process of claim 8where the solid nanoscale inorganic particles are particles of SiO₂,TiO₂, ZrO₂, ZnO, Ta₂O₅, SnO₂, Al₂O₃, and mixtures thereof.
 10. A processof claim 1 where the polymerizable and/or polycondensable surface groupsare acrylic, methacrylic, vinylic, allylic or epoxy groups.
 11. Aprocess of claim 1 where the solid nanoscale inorganic particles used instep (a) are prepared by surface modification of solid nanoscaleinorganic particles using at least one compound containing apolymerizable and/or polycondensable group.
 12. A process of claim 1where the solid nanoscale inorganic particles are prepared by a sol-gelprocess.
 13. A process of claim 1 where the solid nanoscale inorganicparticles of step (a) additionally have fluorinated surface groupspresent thereon.
 14. A process of claim 13 where the fluorinated surfacegroups have the formula R_(f)—CH₂—CH₂—, wherein R_(f) is aperfluoroalkyl radical having 2 to 12 carbon atoms.
 15. A process ofclaim 1 where step (c) is carried out in the presence of polymerizableand/or polycondensable monomeric or oligomeric species not bonded tosaid solid nanoscale inorganic particles.
 16. A process of claim 1 wherestep (c) is carried out in the presence of a thermoinitiator and/or aphotinitiator.
 17. A process of claim 1 where step (c) includes aphotochemical polymerization and/or polycondensation.
 18. A process ofclaim 1 where the substrate of step (b2) is a plastic, metal, or glasssubstrate.
 19. A nanostructured moulded article prepared by the processof claim
 1. 20. A process for producing a nanostructured layer on aplastic substrate, comprising the following steps: (a) providing adispersion of nanoscale metal oxide particles in a system comprising atleast one hydrolyzable silane containing at least one polymerizableand/or polycondensable group at a concentration of at least 15% by wt.,and subsequently prehydrolyzing the at least one hydrolyzable silane;(b) applying the composition of step (a) to a plastic substrate to forma layer; and c) photochemically curing the layer of step (b).
 21. Aprocess of claim 20 where the nanoscale metal oxide particles areparticles of Al₂O₃, TiO₂ and/or ZrO₂.
 22. A process of claim 20 wherethe hydrolyzable silane contains an acrylic, methacrylic, vinylic, orallylic group.
 23. A process of claim 20 where the concentration of thenanoscale metal oxide particles in the dispersion of step (a) is atleast 20% by wt.
 24. A process of claim 23 where the concentration ofthe nanoscale metal oxide particles in the dispersion of step (a) is atleast 30% by wt.
 25. A process of claim 20 where the prehydrolyzing stepof step (a) is carried out in the absence of separately added organicsolvent.
 26. A process of claim 20 where a photoinitiator is added isadded to the dispersion of step (a) before carrying out step (b).
 27. Aprocess of claim 20 where the plastic of the plastic substrate is apolyacrylate, polymethacrylate, polycarbonate, or polystyrene.
 28. Aplastic substrate provided with a nanostructured layer prepared by theprocess of claim 20.